1. Field
The present specification generally relates to systems and methods for capturing a target gas from a process gas stream and, more particularly, to systems and methods for simultaneous adsorption and desorption of target gas in a thermally integrated manner.
2. Technical Background
Capture of a target gas from a process gas stream comprising one or more gases in addition to the target gas may be accomplished in a number of ways. For example, the capture of the target gas may involve first adsorbing the target gas onto a sorbent material. When the sorbent material is saturated, the target gas may be desorbed from the sorbent material, thereby regenerating the sorbent material for further use. Adsorption is an exothermic (i.e., energy-releasing) process, whereas desorption is an endothermic (i.e., energy-absorbing) process. Thus, adsorption processes respond favorably when low temperatures are maintained, whereas desorption processes respond favorably at increased temperatures. Thermal optimization of any system can be challenging when both adsorption and desorption processes occur within the same system.
Complex systems involving adsorption and desorption of a target gas may include heat exchangers that take away heat produced during the exothermic adsorption process. Then, to release the adsorbed target gas, a chemical potential may be created by increasing the adsorbent temperature (Temperature Swing Adjustment or TSA) or by reducing the partial pressure of the target gas in the surrounding atmosphere (Pressure Swing Adjustment or PSA). During the endothermic desorption process energy may be supplied to the adsorbent material through the heat exchanger, such as in a TSA process, or the temperature of the whole system may decrease if there is no external heat source, such as in a PSA process.
The fabrication of heat exchangers presents several manufacturing challenges, and associated processes involving heat exchangers are energy-intensive. For example, it is possible in a monolith-based system to make selected channel walls impermeable so that heat exchanger fluid is isolated from adsorbent layers. Such a configuration decreases efficiency by dedicating certain channels to coolant only. Moreover, external energy is required to pump coolant fluid and extract heat during adsorption, as well as to provide heat during desorption.
Accordingly, ongoing needs exist for alternative systems and methods for capturing target gases from a process gas stream.